This invention relates to a reciprocating piston internal combustion engine utilizing an air induction arrangement and in particular, to an air induction arrangement utilized on a variable displacement reciprocating piston engine having cylinder deactivation.
Four-stroke, multiple-cylinder, reciprocating piston internal combustion engines used in automobiles are capable of being operated over great speed and load ranges. Those skilled in the art have recognized for years that lower specific fuel consumption is usually achieved when an engine is operated at a relatively high load. This is particularly true for spark ignition engines because throttling losses are minimized when the engine is operated at or near wide open throttle at full load conditions. Unfortunately, engines are frequently required to operate at less than maximum load. When an engine operates at partial load, fuel economy suffers because of the pumping loss. Therefore, it is desirable to avoid partial load operation of the engine.
Engines have been designed that avoid partial load operation by deactivating selected cylinder combustion chambers to allow the remaining active chambers to be operated at higher loads. Such engines are often referred to as variable displacement engines. Deactivation of the cylinders is typically achieved by a lost motion rocker arm assembly which can be selectively disabled, therefore allowing the valves associated with the given cylinder to remain in a deactivated open or closed position regardless of the position of an associated cam shaft.
Reciprocating piston internal combustion engines typically tend to be very loud. To lower the noise associated with such engines, the engine exhaust is connected to a muffler. Reciprocating piston engines also make noise about their inlets. To modify and/or lower the noise associated with the engine inlets, resonators can be provided.
Many variable displacement engines are built in a V configuration, which has two banks of cylinders corresponding to the different arms of the V. One bank comprises a first group of cylinders. A second opposite bank comprises a second group of cylinders. When there is a low power demand on the engine such as when the vehicle is idling or cruising on a highway, only one group of cylinders is operational. During high power demand, such as acceleration, both banks or groups of cylinders will be utilized to power the engine. An example of such an engine is a variable displacement V-10 engine. By selectively disabling one bank of the V-10 engine, the V-10 engine essentially operates as an inline five-cylinder (I5) engine.
Increasingly, vehicle operators are not only concerned with the volume of sound which emanates from the vehicle""s power plant, but also are highly influenced by the quality of sound. In premium luxury vehicles, a quality sound is usually defined as a quiet sound which is least perceptible. In sportier and/or high performance vehicles, a quality sound is a roar that occurs during acceleration. If quality is defined as a quiet sound, sound quality improves as the number of cylinders in an engine increases. If quality is defined as a roaring powerful sound, good sound quality is often achieved with a smaller displacement engine such as a five-cylinder configuration.
When a vehicle is being powered by an I5 engine, a waterfall plot (FIG. 4) of engine noise will show the most dominant acoustic output at a 2.5 engine mode. In a five-cylinder engine, 2.5 cylinders will fire for every single rotation of the crankshaft. Accordingly, the predominant sound power output will be at the 2.5 mode and at multiples thereof at 5 mode and 7.5 mode. In a V-10 engine, the most dominant sound power output (FIG. 3) will be at 5 mode engine order. The V-10 engine can be quieter than a comparable I5 engine (FIG. 5) at the same operating conditions. An I5 engine sound as previously mentioned is considered superior for a performance vehicle. Therefore, if a V-10 variable displacement engine is being utilized, it is desirable that the engine sound like two separate I5 engines rather than one V-10 engine.
To encourage acceptance of vehicles with variable displacement engines, it is desirable that the transition between five-cylinder operation and ten-cylinder operation of the engine be imperceptible to the vehicle driver. When a vehicle with a variable displacement V-10 engine is first started, one bank of cylinders will be deactivated. The engine, when idling, will be in an I5 mode of operation. As the vehicle accelerates, the second bank of cylinders is activated, and the engine will function as a V-10. When the vehicle has fully accelerated to highway speeds, the engine will revert back to an I5 operation to maximize fuel economy.
In order for the transitions to be imperceptible to the driver, it is important that the engine sound the same when operating in an I5 mode of operation or a V-10 mode of operation. Transition between I5 and V-10 modes of operation can occur at any point between approximately 1,500 and 3,000 rpm depending upon other factors programmed into the engine controller. If the transition occurs at approximately 2,100 rpm there will be an approximately 15 decibel difference in the sound of the inlet from the transition between I5 operation and V-10 operation. If is desirable to reduce this differential.
Several techniques are available to match the engine mode sound characteristics between I5 and V-10. One method is to attenuate all inlet noise. However, this method requires utilization of very large resonators and eliminates all sound character from the intake inlet. A second method attempts to match the V-10 sound quality while the engine operates in the I5 mode. This method also requires large resonators, which were found to be undesirable. Additionally, the vehicle engine sound assumes more of the sound quality of V-10 engine operation. As mentioned previously, the V-10 sound output was considered to be undesirable.
Referring back to FIG. 5, if the engine has one inlet in I5 wide open throttle (WOT) operation the noise output of the inlet is generally higher. The V-10 WOT operation of the engine will have a lower noise output due to the acoustic cancellation in the induction arrangement.
In a move towards a preferred embodiment of the present invention, a second separate inlet is provided. The inlets are connected to a dual plenum intake manifold. The cylinders on one engine bank are connected to a first plenum and the first intake. The cylinders on the second engine bank are connected to the second plenum and the second intake. This air induction arrangement in the I5 mode has the sound of an I5 engine. However, in the V-10 mode, when both cylinder banks are operating, acoustic cancellation can occur resulting in the aforedescribed V-10 sound output. Accordingly, transition from I5 mode to V-10 mode tends to have the aforedescribed high decibel differential in its sound output.
It is desirable to provide a variable displacement engine which has the sound characteristic of an engine with half the cylinders. It is also desirable to provide a variable displacement engine that has transition from partial utilization of the cylinders to full utilization of the cylinders that is virtually imperceptible to the vehicle driver.
In a preferred embodiment, the present invention has an engine with an air induction arrangement having a first inlet. The first inlet is connected to a first group of cylinders via a first throttle and a first plenum. A second inlet is connected to a second plenum and a second group of cylinders.
At low engine power demand, the engine operates with the first group of cylinders. Selectively, when more power is required, the engine will additionally operate the second group of cylinders. During the low power operation, air will be induced into the first plenum via the first inlet and first throttle. This will cause the engine to operate as an I5 mode (assuming the engine is a V-10). When the engine requires more power, the second group of cylinders will also operate the engine and air will be induced into the second plenum via the second inlet and second throttle.
The cancellation of acoustic output between the first and second inlets is reduced so that when the engine is operating with the first and second groups of cylinders, it sounds like an engine operating with only the first group of cylinders. Accordingly, the transition between I5 and V-10 modes of operation is less perceptible or totally imperceptible to the vehicle operator. Cancellation of acoustic output between the inlets is reduced by either physically separating the inlets or, as described in one embodiment of the present invention, the first inlet is selected to have a slightly smaller diameter than the second inlet. Accordingly, cancellation of acoustic output between the inlets is greatly reduced and this reduction is generally constant over a large engine rotational speed operation range.
The present invention brings forth an advantage of a variable displacement engine whose sound output does not materially change during the transition from partial cylinder operation to full cylinder operation. Additionally, the variable displacement engine of the present invention has an advantage of giving a sportier sound quality which allows the engine to have a roar during acceleration which is typically not available with engines having such a large amount of cylinders.
Other advantages of the present invention will become more apparent to those skilled in the art from a reading of the following detailed description and upon reference to the drawings.